1. Field of the Invention
The present invention relates generally to organic/polymer chemistry, and more particularly to molecules such as polymers, that can incorporate triptycenes and iptycenes.
2. Description of Related Art
Many materials and molecules have rigid structures that can be said to be shape-persistent. Aromatic, conjugated and polycyclic structures are typically their principle building blocks, and are the base architectures that provide the anisotropic characteristics of liquid crystals and high strength polymers. In general, these materials have flat two-dimensional structures and low degrees of internal free volume.
In contrast, chemical structures that have relatively high internal free volumes include those of the iptycenes. Typical applications of iptycenes and related structures have been as groups to prevent aggregation of polymers, thermally stable elements in structural polymers, and as a rigid scaffolds to define a molecular receptor.
The invention comprises materials, compositions and methods that have, as one element, a shape-persistent material with a high degree of internal free volume. In another aspect, the invention comprises new materials, or known shape-persistent materials with high degree of internal free volume that are used in new ways.
In one embodiment, the invention provides a composition comprising a ladder polymer or an oligomer that comprises an iptycene. In another embodiment, the invention provides a composition comprising an iptycene, having a molecular weight in excess of 2,000 daltons. The composition comprises a shape-persistent molecule containing bridgehead atoms, with molecular structures radiating from the bridgehead atoms in three directions and extending outwardly therefrom such that each defines a van der Waals contact of furthest point from the bridgehead atoms of no less than 3.5 xc3x85. The composition can be a linear polymer or a ladder polymer. In one embodiment, the composition is arranged as a dielectric material in an electronic component. When the composition defines a polymer, the polymer can include a backbone having backbone atoms bonded to other backbone atoms, where bonds involving the backbone atoms are not freely rotatable.
The compositions described herein have a high degree of free volume, for example, at least 20%, 30%, 50%, 70% or 90% free volume, as defined below. Shape-persistent molecules with higher free volume can be used to improve alignment or orientation of one molecule to another. A variety of exemplary structures, both of polymeric shape-persistent molecules or monomers that can be used alone or can be polymerized to form polymers are described herein. It is to be understood that all examples of monomers and/or polymers described herein can be used in connection with any aspect or embodiment of the invention in which a shape-persistent molecule or polymer is desirable.
Where polymers of the invention are provided, they can comprise polymer chain units including chemical functionality allowing the formation of grafts. One polymer includes a grafted polymer including iptycene or non-iptycene units grafted onto polymer chains. Or, iptycene and non-iptycene units can be used in combination in such a graft polymer. Polymers can be formed of monomer units, each including two reactive sites, one of which has reacted with another monomer unit to form the polymer backbone, and another of which is available for grafting after formation of the polymer.
As noted, high free-volume, shape-persistent structures can be used as dielectrics. Dielectric structures having a dielectric constant of about 1.9 or less, preferably 1.7, 1.5 or 1.2 or less are provided in accordance with the invention.
The invention provides negative Poisson ratio (NPR) materials. One set of materials includes polymeric shape-persistent structures having small pores, on the order of 3-6 xc3x85 in size, through which a second polymeric material can be threaded to form an interpenetrating network. For example, polyiptycenes will form porous materials, as described below, and a generally planar structure perpendicular to the pores. Where a flexible polymer interpenetrates pores of such structures, applying tension to the interpenetrating polymer can cause the polyiptycenes to align in a generally planar/planar fashion, causing a greater degree of order between generally planar polyiptycene structures, thereby increasing the free volume of the overall structure. This can define a NPR material. That is, when tension is not applied to the interpenetrating polymer, the generally planar polyiptycene structures are allowed to rotate or otherwise orient themselves in a low-energy, random configuration. This will tend to minimize free volume. When tension is applied to the interpenetrating polymer, the generally planar polyiptycene structures will be moved into alignment generally parallel to each other, forming a higher-energy, higher free-volume structure. The interpenetrating polymer can be, for example, a conjugated polymer, an elastomer, or the like.
In another aspect, the invention comprises a first component comprising a first, porous shape-persistent polymeric component, and a second polymeric component forming an interpenetrating network. The network permeates the pores of the first polymeric component.
As mentioned above, shape-persistent molecules of the invention can assist in alignment or orientation of one molecule to another. This can be important in optical technology, such as liquid crystal display (LCD) technology. Liquid crystals are molecules which, when non-aligned with each other, are generally transparent. When an electric field is applied, they can be made to orient in alignment with each other, becoming opaque. Color LCD displays include liquid crystal molecules in conjunction with chromophores, including dyes. Contrast in color LCD displays is maximized (a significant advantage) when chromophores can be made to align with LCD molecules. The present invention involves including a shape-persistent molecule in conjunction with a chromophore in a LCD matrix. The shape-persistent molecule can assist the alignment of the chromophore with LCD molecules. For example, a shape-persistent molecule with a high degree of free volume can be covalently attached to a dye and combined with LCD molecules. When energy is applied to the system which generally causes LCD molecules to align with each other, the shape-persistent molecule can interact with the LCD molecules to maximize alignment of the dye with the LCD molecules. This is described in greater detail below and demonstrated in the examples section. This increase in alignment between two molecules with the assistance of a shape-persistent molecule can be used in essentially any arrangement in which improved alignment is desired, not limited to LCD systems.
Accordingly, in one embodiment the invention provides a composition including a chromophore, a shape-persistent molecule having at least 20% free volume, and a host material within which the shape-persistent molecule self-orients. The host material can be, for example, LCD molecules.
In another embodiment, the invention involves a method comprising providing a first molecular species in association with a shape-persistent molecule having a high degree of internal free volume, and a second molecular species. The method involves causing a change in orientation of the second molecular species and allowing the shape-persistent molecule to thereby alter the orientation of the first molecule in response to the change in orientation of the second molecule. An example of this involves a second molecular species comprising LCD host material and a first molecular species comprising a dye covalently bonded to an iptycene. A change in orientation of the LCD host material (e.g., alignment) causes a change in orientation of the dye as directed by the iptycene, namely, the dye can orient in alignment with the LCD host material. Translation, as well as or instead of orientation, can be affected in this manner as well.
Shape-persistent molecules of the invention typically include at least two aromatic rings, each parallel to a common axis in a lowest energy state of the composition.
In another embodiment, the invention comprises a composition including a plurality of liquid crystalline species. Each has a primary axis aligned so as to together define an average axis of the liquid crystalline species primary axes. A plurality of chromophores are provided, each having a primary axis aligned so as to together define an average axis of the chromophore primary axes. The alignment of the individual chromophores relative to the average axis of the chromophore primary axes includes less variation than the alignment of the individual liquid crystalline species relative to the average axis of the liquid crystalline species primary axes.
In another embodiment, the invention provides a size-exclusion article. As used herein, xe2x80x9csize-exclusion articlexe2x80x9d defines a material that will allow the passage of species of a particular size, but not allow passage of species larger than that size. Examples include filters, such as zeolite structures, etc. Size-exclusion articles of the invention can be defined by any species described herein that will form pores, such as a ladder polymer or oligomer comprising an iptycene, having pore sizes noted herein.
Compositions of the invention can enhance the modulus of polymeric compositions. This can be effected by blending compositions of the invention into existing polymer blends, forming copolymers, including compositions of the invention, or grafting compositions of the invention onto existing polymers. Accordingly, one composition of the invention includes a first component that is a polymer including an iptycene, and a second component. The second component typically is a high molecular weight linear polymer, such as one having a molecular weight greater than 5,000, 10,000 or 20,000 daltons. The composition has a greater strength compared to a composition that is identical, with the exception that it does not include the iptycene-containing polymer.
In another aspect, the invention comprises a chromophore and a shape-persistent molecule including at least two aromatic rings, each parallel to a common axis in a lowest energy state of the composition.
In another aspect, the invention comprises a composition comprising a shape persistent moiety with a high degree of internal free volume and a chromophore.